1. Field of Invention
The present invention relates generally to a method of producing particles via solvent extraction using a supercritical fluid, wherein a solute is dissolved in a solvent to form a solution, and the solution is dispersed in an immiscible or partially miscible liquid to form an emulsion, and the solvent is extracted from the emulsion.
2. Description of Related Art
Particles are conventionally produced by forming a solution of desired material in an organic solvent, which is then emulsified with large quantities of water. The desired material is then precipitated from the emulsion in the form of fine particles either by evaporation of the solvent or by extraction using another organic solvent. Removal of the organic solvent from the micelles of the emulsion leads to supersaturation, which in turn results in the precipitation of the desired material as fine particles.
This process has several drawbacks. First, the process proceeds at an extremely slow rate, exceeding several hours in most instances. Ensuring low residual solvent levels requires undesirably long evaporation times. Second, organic solvent extraction processes are difficult to scale up and require the use of a large amount of solvent, which results in a large waste stream. Furthermore, concerns have been raised in recent years about possible environmental and health affects arising from the use of certain solvents which are difficult to remove completely and are sometimes retained as a residual material in the final product.